how detect "OnRaycastOut"

When my characterMesh turns towards a cube, it turns gray. When I move my characterMesh the other way (he now faces a different cube), the new cube should turn gray. I have come that far. I would like the old cube to turn to it's original color. Any ideas?

 using UnityEngine;
 using System.Collections;
 
 public class DmgCube_scr : MonoBehaviour {
     
     Color originalColor;
     GameObject target;
     GameController_scr gc_scr;
     
     
     void Start () {
         originalColor = gameObject.renderer.material.color;
         gc_scr = GameObject.Find ("GameController").GetComponent<GameController_scr>();
     }
     
 
     void Update () {
 
         // ::::::::::::::::::::::::::::::::::::::::::::::: TARGETING :::::::::::::::::::::::::::::::::::::::::::
         Ray targetingRay = new Ray(transform.position, transform.TransformDirection (Vector3.forward));
         RaycastHit targetHit;
         
         if(Physics.Raycast (targetingRay, out targetHit, 1f))
         {
             if(targetHit.transform.gameObject.tag == "cube")
             {
                 target = targetHit.transform.gameObject;
                 target.renderer.material.color = Color.gray;
             }
         }
     }
 }